This relates generally to a device for heating articles and organisms and in particular to a device for rendering harmless or destroying organisms containing nucleic acids and/or proteins by transmission of microwaves radiation into a chamber containing the articles and/or organisms wherein such radiation is generated by a plurality of magnetrons configured to avoid cold spots.
It is known that living cells and organisms as well as small viruses and other organisms containing proteins and nucleic acids can be destroyed or rendered harmless by the action of chemical or physical substances, whereby they lose their toxicity. Infected material may be sterilized by physical methods, such as exposure to heat, radiation (beta rays, X-rays, gamma rays, UV radiation) chemical methods and special filtration, in which the organisms are physically retained. Exposure to a sufficient amount of heat for a sufficient time irreversibly damages and renders harmless the proteins and/or nucleic acid contained within the infected material. Thus, all growth and reproductive functions of the organism exposed to such heat are destroyed. Devices for exposing material to heat for sterilization purposes are presently routinely used worldwide in the medical and industrial fields. Such devices are also frequently employed for destroying a wide variety of infectious waste prior to final disposal and for preventing harm to disposal personnel as well as to the general public.
Known devices which expose infected material to heat typically operate either by the method of hot air sterilization or by autoclaving. In these methods, heat (hot air sterilization), or steam under pressure (autoclaving) must be supplied from an external environment to the infected material to be sterilized, so that successful sterilization may only be attained by precisely following exacting procedures.
Although these two methods of heat sterilization are generally considered reliable and result in relatively complete sterilization of the infected material, an enormously high outlay of energy and time is required in order to adequately sterilize the infected material. Furthermore, a most unpleasant and unavoidable odor is generally produced by these methods.
Exposure of the infected material to radiation, and in particular to radioactivity, may render the infected material harmless but is hardly practicable for sterilization of infected material because of high industrial and safety engineering costs associated with use of sufficiently radioactive substances.
Filtration of the infected material, in which the organisms must be physically collected in a filter in especially high concentration is not a complete nor adequate solution as the collected organisms must still be disposed of. Apart from this, the method is largely limited to liquids, and possibly gases, but cannot be employed for organisms found on solid carriers.
In addition to these methods and devices, chemical methods in which disinfectant chemicals are employed for sterilizing infected material may be used. However, chemical methods are suitable primarily for surface disinfection and for disinfecting of interior walls of hollow chambers into which the disinfectants can be introduced in a controlled manner.
A final method of destroying or rendering harmless organisms containing nucleic acids and/or proteins comprises exposing such organisms or articles infected with such organisms to microwave radiation.
Living structures exposed to microwave radiation undergo a heating of fluids from within the structure, such heating exceeding the boiling point of the fluids and resulting in death or destruction of the organism. A requirement of microwave sterilization is that all organisms present in the sterilization chamber be exposed to sufficient microwave energy. In conventional devices, precautions have not been taken to avoid the occurrence of the so-called "cold spots." The avoidance of such cold spots is essential when infected articles are placed in the sterilization chamber to be uniformly exposed to microwave radiation and thus sterilized. Since the microwave radiation is transmitted for a relatively short time only, any heating by heat conduction in the infected material itself is without practical significance and will not significantly aid in the sterilization of the material.
In addition to problems associated with supplying inadequate microwave radiation to certain areas of the sterilization chamber, known microwave devices often leak microwave radiation to the environment external to the device.
More particularly, known microwave devices will in general exhibit scattering radiation, i.e. a portion of the high frequency radiation generated by the device will leave the system at points not completely impervious to high frequency radiation. Most of this leakage radiation is typically given off through door crevices and seals. Furthermore, such leakage radiation is not limited to microwave devices for performing sterilization but exists in practically all microwave generating devices.
The high-frequency leakage radiation represents a potential hazard to the operator of the device as well as others in close vicinity. For this reason, there are internationally set standards on maximum allowable peak limits of radiation emitted from microwave devices. Thus a device when sold must not emit to the environment more than a prescribed output density of microwave radiation.
It is known, however, that leakage of microwave radiation may be minimized through utilization of suitable materials and constructing the device in accordance with proper specification. However, regardless of the quality of materials or construction or even the initial minimization of microwave radiation, the materials and components constructed therefrom are all subject to aging and/or wear resulting in increased microwave radiation leakage. Moreover, such increased microwave leakage typically occurs without the knowledge of the operator, thereby potentially exposing the operator or other personnel to increasingly severe levels of radiation resulting in irreversible harm.
In particular, known devices and methods exist whereby the amount of leakage of microwave radiation may be tested. Unfortunately, such devices are not generally available to the operator, nor are there generally any statutory provisions calling for periodic inspection of a microwave device including measurement of leakage radiation. Furthermore, the cost of such an output density measuring system is often prohibitive and thus such devices are generally not owned by most microwave device owners. Even if microwave devices are repeatedly subjected to testing, during operation of the device, such as in the period between two successive tests, the operator can have no complete assurance that prior leakage levels accurately reflect present microwave leakage levels. For example, rubber gaskets may become damaged and indeed do generally degrade with time. Such damage may not become apparent until the next inspection of the device. In the interval, the operator of the device would have been exposed to the microwave radiation without protection.
Illustrative of prior art sterilization methods is German Patent 3430673 which discloses a sterilization process in which the material to be sterilized is passed through a hollow conductor between two synchronously running conveyor belts. Unfortunately, what is generally referred to as "cold spots", i.e., portions of the hollow conductor not receiving sufficient sterilizing radiation, are often developed in such a hollow conductor. Such cold spots prevent complete sterilization of the material in practice and lead to an increased risk of infection and the like. Furthermore, this device is complicated in structure and involves problems associated with shielding the outside environment from the microwave radiation.
European Patent Application 0 116 921 discloses a sterilization system for infusion of a liquid from an external closed container into a patient. More specifically, the external closed container is provided with a first conduit connected to a coupling which is also connected to the patient by way of a second conduit. A small volume of liquid is permitted to flow to the coupling whereupon a guided wave member is then placed over the coupling and emits radiation to destroy any bacteria present in the coupling. Unfortunately, this device is limited to sterilizing liquid contained within a coupling connecting two conduits. It is often desirable to sterilize other materials and in fact it is generally necessary to sterilize medical wastes in order to destroy organisms such as bacteria, viruses and spores contained therein. However, known devices and methods are not capable of adequately disinfecting or sterilizing medical waste and the like prior to disposal in a land fill or combustion facility so as to avoid endangering disposal personnel as well as the general public.
U.S. Pat. No. 2,550,584 discloses a milk pasteurization system in which milk continuously flows through a heat exchanger and through a fluid cooled high frequency electronic tube heater. The high frequency heater comprises a cylindrical member having an input end and an output end. Heat from the high frequency heater is used to preheat the milk in the heat exchanger. However, this device is limited to pasteurizing milk.